1. Field of the Invention
The present invention relates to a digital magnetic recording and/or reproducing apparatus, and in particular to a digital magnetic recording and/or reproducing apparatus adopting variable length coding data compression for magnetically recording a digital video signal such as a television signal.
2. Description of the Prior Art
In a magnetic recording and/or reproducing apparatus such as a D1-VTR for magnetically recording a digital television signal, in order to achieve improved error correction and error modification capabilities, the order of image data to be recorded onto a track of a recording tape differs from the order in position of the image data located in a frame.
Meanwhile, there have been a lot of reports concerning a magnetic recording and reproducing apparatus for digitally recording compressed data obtained by compressing a television signal utilizing a high-efficiency coding technique for bit rate reduction. For instance, there is a reference literature in the art by Yamamitsu et al.: "A Study on Trick Plays for Digital VCR", IEEE Trans. Consum. Electron, Vol. 37, No. 3, pp. 261-266 (August, 1991). As described in the above-mentioned literature, it is general to use a variable length coding technique for high-efficiency coding.
In a variable length coding method, an orthogonal transformation is effected on data of each image block which is composed of, for example, adjoining 8 pixels.times.8 lines, and then the resulting orthogonally transformed data is compressed into a specified data length every image block group composed of a specified number of image blocks. Furthermore, for the purpose of achieving an increased compression efficiency, before effecting the variable length coding operation, the order of the image blocks in each image block group included in a frame is rearranged so that the image blocks are located apart from each other in a frame. In such a magnetic recording and reproducing apparatus, the order of image blocks in a frame differs from the order of the image blocks corresponding to the data recorded on a video track of the magnetic recording tape.
Meanwhile, when reproducing data by the magnetic recording and reproducing apparatus in a high-speed playback mode, only a part of the data recorded on the video tracks of the magnetic tape is reproduced. Therefore, when effecting a high-speed playback operation to a magnetic tape on which compressed data are digitally recorded, the resulting playback picture is formed with combination of the image data corresponding to a plurality of frames recorded on the magnetic tape.
Furthermore, the locations of a plurality of image blocks reproduced from one video track are apart from each other in position of the frame.
For the above reasons, image data of different frames are combined in a mosaic pattern in the high-speed playback mode, which also results in a significantly unsightly playback picture on the screen.